A conventional water bottle cap with a hose is disclosed in CN 201381022 and includes a cap and a hose, wherein the cap has a recessed area from which a tube is extended and the hose is mounted to the tube. A suction unit is pivotably connected to the recessed area and includes a pivot and a mouthpiece which is securely connected to the pivot. The mouthpiece has a passage which communicates with the tube. The pivot includes a protrusion which positions the suction unit when the suction unit is in closed position. The benefits of the cap is that the protrusion well positions the suction unit when not in use so that the liquid in the bottle cannot not flow out from the suction unit. However, the protrusion tends to be worn out after frequent uses and is loosened or even disengaged from the recess in the recessed area. This restricts the reliability and durability of the product. Besides, there is no dust cap provided and the users have to directly operate the suction unit and directly touch the suction part which may be contaminated.
The present invention intends to provide a bottle cap assembly to improve the shortcomings of the above mentioned conventional cap assembly.